This invention pertains to side bearings for a railway truck such as the well known three piece truck as commonly used in freight service.
Typically, a rail car body is rotatably supported at its opposite ends on the center bowls of respective truck bolsters. Each such bolster extends transversely of the track and is supported at its opposed longitudinal ends by springs carried by the respective truck side frames.
A railway truck bolster commonly carries a pair of side bearings which are spaced from the bolster center bowl toward the respective longitudinal ends of the bolster, and are secured thereto by mechanical fasteners such as bolts. Each side bearing engages a wear plate mounted on the car body to support the car body laterally outward of the bolster center bowl and thereby limit lateral car body rocking.
Certain types of side bearings, known as constant contact side bearings, are installed in a preloaded state to maintain continuous forceful engagement with the car body wear plate. A constant contact side bearing slides on the car body wear plate in operation to thereby provide frictional energy dissipation and assist in controlling the destructive, cyclic truck motion known as hunting. As the hunting phenomenon is well known and is discussed at length in the prior art, detailed description thereof is unnecessary here. Suffice it to note that in many known side bearings, the normal force for frictional energy dissipation is provided by resilient deformation of coil springs or other compliant elements such as elastomeric columns. The prior art of side bearings with resiliently deformable bearing elements includes those disclosed in, for example, U.S. Pat. Nos. 3,295,463, 3,957,318, 4,080,016, 4,712,487, 4,998,997, 5,207,161, 5,386,783, and 5,601,031.
The present invention contemplates a side bearing wherein a side bearing cage is provided with through openings in the cage base to accommodate fasteners, for securing the cage to a railway truck bolster. One such opening can be provided in a cavity in the cage which houses an upstanding elastomeric column, or similar resiliently deformable bearing element. Such opening can be generally coaxial the center of the bearing cavity. Additionally, such opening can extend through an upwardly projecting boss located centrally in the base of the side bearing cage such that the boss can serve to locate and/or retain a lower end of the upstanding elastomeric column. Alternatively, the head of a fastener used to secure the bearing cage to the bolster via the opening can locate and/or retain the end of the bearing column.
The elastomeric bearing element can similarly be located and retained at its upper end by a cap member which engages the side bearing cage so that transverse loadings generally pass to the bolster from the cap member through the side bearing cage and are generally not carried by the elastomeric bearing element.
The structural configuration of the side bearing cage also permits mounting on a bolster such that a solid or rigid bearing element housed in the bearing cage, a roller for example, can be located near the midpoint of the bearing cage mounting points on the bolster, and thus typically the bolster centerline, which can be a useful feature in view of benefits related to symmetrical bearing loading.